The CD30 cell surface molecule is a member of the tumor necrosis factor receptor (TNF-R) superfamily. This family of molecules has variable homology among its members and includes nerve growth factor receptor (NGFR), CD120(a), CD120(b), CD27, CD40 and CD95. These molecules are typically characterized by the presence of multiple cysteine-rich repeats in the extracytoplasmic region (de Bruin, P. C., et al. Leukemia 9:1620-1627 (1995)). Members of this family are considered crucial for regulating proliferation and differentiation of lymphocytes.
CD30 is a type I transmembrane glycoprotein with six (human) or three (murine and rat) cysteine-rich repeats with a central hinge sequence. CD30 exists as a 120 kDa membrane molecule which develops from an intercellular precursor protein of 90 kDa. It is shed from the cell surface as a soluble protein (sCD30) of approximately 90 kDa. Shedding of sCD30 occurs as an active process of viable CD30 cells and is not merely caused by the release from dying or dead cells. cDNAs encoding the CD30 protein have been cloned from expression libraries of the HLTV-1 human T-cell line HUT-102 by immunoscreening with monoclonal antibodies Ki-1 and Ber-H2 (Schwab, U., et al. Nature 299:65 (1982)). The mouse and rat CD30 cDNA has been found to encode 498 and 493 amino acids, respectively. Human CD30 cDNA encodes an additional 90 amino acids, partially duplicated from one of the cysteine rich domains. The CD30 gene has been mapped to 1p36 in humans and 5q36.2 in rats.
CD30 is preferentially expressed by activated lymphoid cells. Specifically, stimulation of CD30 in lymphoid cells has been shown to induce pleiotropic biological effects, including proliferation, activation, differentiation and cell death, depending on cell type, stage of differentiation and presence of other stimuli (Gruss, H. J. et al., Blood 83:2045-2056 (1994)). CD30 was originally identified by the monoclonal antibody Ki-1, which is reactive with antigens expressed on Hodgkin and Reed-Sternberg cells of Hodgkin's disease (Schwab et al., Nature 299:65 (1982)). Accordingly, CD30 is widely used as a clinical marker for Hodgkin's lymphoma and related hematological malignancies (Froese et al., J. Immunol. 139:2081 (1987); Carde et al., Eur. J. Cancer 26:474 (1990)).
CD30 was subsequently shown to be expressed on a subset of non-Hodgkin's lymphomas (NHL), including Burkitt's lymphoma, anaplastic large-cell lymphomas (ALCL), cutaneous T-cell lymphomas, nodular small cleaved-cell lymphomas, lymphocytic lymphomas, peripheral T-cell lymphomas, Lennert's lymphomas, immunoblastic lymphomas, T-cell leukemia/lymphomas (ATLL), adult T-cell leukemia (T-ALL), and entroblastic/centrocytic (cb/cc) follicular lymphomas (Stein et al., Blood 66:848 (1985); Miettinen, Arch. Pathol. Lab. Med. 116:1197 (1992); Piris et al., Histopathology 17:211 (1990); Bums et al., Am. J. Clin. Pathol. 93:327(1990); and Eckert et al., Am. J. Dermatopathol. 11:345 (1989)), as well as several virally-transformed lines such as human T-Cell Lymphotrophic Virus I or II transformed T-cells, and Epstein-Barr Virus transformed B-cells (Stein et al., Blood 66:848 (1985); Andreesen et al., Blood 63:1299 (1984)). In addition, CD30 expression has been documented in embryonal carcinomas, nonembryonal carcinomas, malignant melanomas, mesenchymal tumors, and myeloid cell lines and macrophages at late stages of differentiation (Schwarting et al., Blood 74:1678 (1989); Pallesen et al., Am J. Pathol. 133:446 (1988); Mechtersheimer et al., Cancer 66:1732 (1990); Andreesen et al., Am. J. Pathol. 134:187 (1989)).
Since the percentage of CD30-positive cells in normal individuals is quite small, the expression of CD30 in tumor cells renders it an important target for antibody mediated therapy to specifically target therapeutic agents against CD30-positive neoplastic cells (Chaiarle, R., et al. Clin. Immunol. 90(2):157-164 (1999)). However, while the results obtained to date clearly establish CD30 as a useful target for immunotherapy, they also show that currently available murine antibodies do not constitute ideal therapeutic agents.
Accordingly, the need exists for improved therapeutic antibodies against CD30 which are effective at treating and/or preventing diseases mediated by CD30.